I was begging them to implement this back in November of 2014, and almost 2 years later, there has been NO advancements in this area at all. It is the reason we have moved away from SmartMail for most of our clients. This email platform is just too limited as a solution for hosting email for multiple clients at different locations. While the LDAP solution is actually quite easy to implement, SM has instead chosen to focus more on making things 'pretty' instead of more functional. We even offered to pay for this option to be added to SM, as well as to provide us the source code so that we can add it into the code for them at NO COST, which they would have benefited greatly from, but they are just not interested in growing their feature set. Their main focus is on appearance and 'cool looking' stuff instead.
They could VERY easily plug in open source code from places like OpenLDAP and YoLinux to accomplish this upgrade within a day or two, but after two years, it's obvious that they are not interested in growing. Move on to a different platform, and quit wasting your money on their constant "upgrades".